Bi-stable brake

ABSTRACT

A bi-stable brake having an annular spring biased cap armature member with permanent magnets affixed thereto slidable along its axis between an annular disk or plate fixed to a rotatable shaft and a fixed annular electromagnet with a small air gap therebetween to provide engagement of the cap member and the plate initiated by a pulse of current in one polarity through the electromagnet to brake the shaft against rotation maintained by the spring bias and to provide disengagement of the cap member and plate by a pulse of current of opposite polarity to engage and hold the permanent magnets and electromagnet together thereby braking and freeing the shaft in either of two states without continuous electromagnet energization.

United States Patent 1191' McKinley et a].

[ June 26, 1973 BI-STABLE BRAKE 3,512,618 5/1970 Schafer 188/161 [75]Inventors: David W. McKinley; James K.

. Primary ExammerDuane A. Reger Attorney-R. s. Sciascia and P. s.Callignon [73] Assignee: The United States of America as 1 representedby the Secretary of the [57] ABSTRACT washmgwnt DC A bi-stable brakehaving an annular spring biased cap 2 Filed; Oct 4 197 armature memberwith permanent magnets affixed I thereto slidable along its axis betweenan annular disk [21] Appl- 1861000 or plate fixed to a rotatable shaftand a fixed annular electromagnet with a small air gap therebetween to52 U.S. Cl. 188/171, 192/18 B Provide snsagement of the p member and thePlate 511 1111. c1 B60t 13/04 initiated y a Pulse of current in one p ythrough [58] Field of Search 188/161, 164, 171; the electromasnet tobrake the shaft against rotation 92 3 3 34 C, 4 PM maintained by thespring bias and to provide disengagement of the cap member and plate bya pulse of current 5 References Cited of opposite polarity to engage andhold the permanent UNITED STATES PATENTS magnets and electromagnettogether thereby braking and freeing the shaft in either of two stateswithout congsgzx tinuous electromagnet energization. 2:886:1 5/1959Baermann 188/161 UX 4 Claims, 4 Drawing Figures a1 1- 3 52 l O L l 8 31I 11 \dn \2 r I 15 Z 30 BI-STABLE BRAKE STATEMENT OF GOVERNMENT INTERESTThe invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to electromagnetbrakes or clutches and more particularly to bi-stable brakes or clutchesrequiring no, electromagnet energization to hold the brake or clutch ineither state.

Prior known such electromagnetic brakes or clutches requireelectromagnet energization to retain the device in one or the other ofits braking or clutching and nonbraking or non-clutching states. Poweris consumed continuously to hold the device in one of its states.

SUMMARY OF THE INVENTION In this invention an armature, ring or annularclutch cap member is slidable along its axis a very limited amount withconfinement between a plate or annular member fixed to a shaft and anelectromagnet element. The armature ring is spring biased away from theelectromagnet element into engagement with the plate or annular memberto restrain the shaft from rotation. The plate and armature have clutchfrictional portions or brake lining thereon for frictional engagementand the armature or annular clutch member includes a ring of permanentmagnets engageable with the electromagnet. The plate is fixed to theshaft through resilient spokes to permit dampened oscillations of theshaft upon the brake or clutch being engaged. When the electromagnet isenergized by a current of one polarity, the armature will be pulledagainst th spring bias to engage the permanent magnets with theelectromagnet after which the electromagnet can be de-energized, beingthe brake disengaged state. The brake will remain disengaged by thepower of the permanent magnets clinging to the electromagnet polesovercoming spring bias. When the electromagnet is energized by a currentof opposite polarity, the armature or cap member will cause theelectromagnet and permanent magnets to repel each other sufficiently toallow the spring to bias the armature into engagement with the plate orannular member to produce a brake engaged state preventing rotation ofthe shaft. The shaft is protected from sudden inertial stops by theresilient spoke connection between the shaft and the annular platesurface. Accordingly, the current to engage or disengage the brake needonly be applied by a short pulse and the brake will remain in either ofthese states without electrical power. It is accordingly a generalobject of this invention to provide a brake or clutch that requires amere pulse of electrical power to change the state thereof but willremain in either state indefinitely without electrical power.

BRIEF DESCRIPTION OF THE DRAWING These and other objects and theattendant advantages, features and uses of the invention will becomemore apparent to those skilled in the art as a more detailed descriptionproceeds when considered along with the accompanying drawing in which:

FIG. 1 is a diametric cross-sectional view of the bistable brake of thisinvention;

FIG. 2 shows an elevational view along the line 2-2 of FIG. 1;

FIG. 3 shows an elevational face view along the lines 3-3 of FIG. 1; and

FIG. 4 shows the diametrical plan view of the plate with resilientspokes between the outer periphery braking surface and the inner hub toallow natural frequency of damping oscillations.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly toFIG. 1 a base or mounting plate 10 has a shaft 11 journaled therein by africtionless type bearing 12 supporting shaft 11 against end play by anut 14 threaded on shaft 11. The bearing 12 is retained in the support10 by an annular ring 15 or the like held by cap screws 16. Thesupporting plate 10 may have eyelets or other means for attachment to adevice such as the case of a gyroscope or the like where the shaft 11 isattached to one gyroscope gimbal ring. The shaft 11 has an enlargedportion 17, the outer end of which supports a plate 18 held captive by anut 19 on the outer threaded end of shaft 11. Affixed to the supportingplate 10 is a cup member 20 housing an electromagnetic coil 21 havingcontrol leads 22 connected thereto. The cup member 20 is annular havinga central opening 23 through which the enlarged portion 17 of shaft 11extends. Cup member 20 terminates ininner periphery and outer peripherypole pieces 24 and 25 in an annular plane about the electromagnet 26consisting of the cup member 20 with coil 21 therein and pole pieces 24and 25 thereon. The outer periphery of the outer pole piece 25 has ashoulder 27 on which shoulder is attached three or more lightweightstrips 28. The free ends of the strips 28 are attached to a cap member29 with at least three and preferably four or more circular permanentmagnets 30 embedded therein although other configurations will work aswell, such as rectangular magnets. As more particularly shown in FIGS. 2and 3, the permanent magnets 30 are embedded in one face of the cap 29,the diameter of the permanent magnets 30 being sufficient to span thedistance between the inner and outer pole piece ends 24 and 25, as shownin FIG. 2. The permanent magnets 30 are all oriented magnetically on thesame radial direction. The cap member 29 is biased away from theelectromagnet 26 by a spring 31 compressed between a shoulder in the capmember 29 and the mounting plate 10. The spring strips 28, having oneend fastened to the outer pole piece in channel 27 and the other endfastened to the outer periphery of the cap member 29, preventsrotational movement of the cap member. The spring 31 biases the capmember 29 outwardly against the plate 18. An annular brake shoe or brakelining 32 is attached either to the plate 18 or to the outer surface ofcap member 29. It also may be desirable or preferable for someapplications to have two brake linings or two annular frictional ringswith one each attached to one each of the plate member 18 and cap member29. The plate 18 has spokes 33 connecting the peripheralbrake surfacewith the hub to allow the shaft 11 to be stopped by damped oscillationsto avoid damage to the device attached to the shaft, such as a gyroscopegimbal. For some applications it may be desirable to make plate 18 asolid disk. As may be realized from the above description when the capmember 29 is biased outwardly by the spring 31 against the plateOPERATION In the operation of the bi-stable brake let it be assumed thatthe brake is resting in its braking state as shown in FIG. 1, therebeing no current applied through the electromagnet coils 21. The shaft11 is held against rotation since the cap member 29 is held againstrotation by the strips 28. When it is desirable to release the shaft forfree rotation, a pulse of direct current voltage of one polarity isapplied to leads 22 to establish magnetic poles at the inner and outerpole pieces 24 and 25 corresponding to the reversed polarity ofpermanent magnets 30. That is, if the pulse of direct current voltageapplied to leads 22 is such to establish a north pole on the pole piece24 and a south pole on the pole piece 25 to attract the cap member 29,the permanent magnets 30 will all be oriented magnetically such thattheir north poles will be along the larger diameter of cap member 29 andtheir south poles will be around the shorter diameter of cap member 29.This will draw all the permanent magnets 30 into engagement with thepole pieces 24 and 25 and the power of these permanent magnets will besufficient to overcome the compressive strength of spring 31 therebyholding the cap member 29 out of engagement with the plate 18 allowingfree rotation of shaft 11 without any further direct current applied tothe electromagnet coils.

When it is again desirable to place shaft 11 in the braking state, it isonly necessary to apply a pulse of direct current in the oppositedirection to polarize the pole pieces 24 and 25 to make 24'the southpole and 25 the north pole magnetically. This condition will cause thepole pieces 24 and 25 to repel the permanent magnets 30 whereupon thespring 31 will again bias the cap member 29 against the plate 18 placingthe shaft in the braking state. If the shaft 11 is in a rotatingcondition at the time the brake is placed in its braking state, theresilience of spokes 33 in the plate 18 will dampen out oscillations inthe shaft 11 to prevent damage to any instrument coupled to the shaft11, such as a gyroscope gimbal ring. Accordingly, the brake, when placedin its braking state, will bring shaft 11 to a stop in a resilient ordampened manner. Either the braking state or the non-braking state ismaintained without any external voltage supply, it only being necessaryto apply a direct current voltage pulse to establish either state orcondition of the brake.

While many modifications may be made in the constructional details toaccomplish the assembly shown and described, it is to be understood thatwe desire to be limited only in the scope of the appended claims.

We claim:

1. A bistable brake device comprising:

an annular electromagnet having inner and outer annular poles and havinga spring biased concentric non-rotatable armature with permanent magnetsaffixed thereto;

a rotatable shaft having an annular disk plate on the opposite side ofsaid armature from said electromagnet providing a small air space oftravel for said armature along the axis of said electromagnet engageablebetween said disk and said electromagnet, said disk plate havingconcentric hub and rim joined by a plurality of spokes to providedampened oscillations when said disk plate is braked;

friction material on at least one of the engageable surfaces of saiddisk and armature; and

leads to said electromagnet for applying direct current pulses ofopposite polarity thereto, a current pulse of one polarity beingeffective to attract said armature to said electromagent where it clingsby the attractive force of said permanent magnets, and a current pulseof the other polarity being effective to cause the electromagnet torepel said permanent magnets to allow said spring force to hold saidarmature against said disk braking any rotative action of said shaftwhereby the brake is engageable and disengageable respectively by anelectric pulse of opposite polarity. I

2. A bi-stable brake device as set forth in claim 1 wherein saidpermanent magnets affixed to said armature cap are oriented withpolarity radially the same.

3. A bi-stable brake device as set forth in claim 1 wherein said springbiased concentric non-rotatable armature is held against rotation withrespect to said electromagnet by light weight leaf material stripshaving opposite ends attached respectively to said outer annular polepiece and the outer periphery of said armature.

4. A bi-stable brake device as set forth in claim 3 wherein said springbiased concentric non-rotatable armature is spring biased by acompression spring around said shaft supported within said innerelectromagnet pole.

it 1: s s

1. A bistable brake device comprising: an annular electromagnet havinginner and outer annular poles and having a spring biased concentricnon-rotatable armature with permanent magnets affixed thereto; arotatable shaft having an annular disk plate on the opposite side ofsaid armature from said electromagnet providing a small air space oftravel for said armature along the axis of said electromagnet engageablebetween said disk and said electromagnet, said disk plate havingconcentric hub and rim joined by a plurality of spokes to providedampened oscillations when said disk plate is braked; friction materialon at least one of the engageable surfaces of said disk and armature;and leads to said electromagnet for applying direct current pulses ofopposite polarity thereto, a current pulse of one polarity beingeffective to attract said armature to said electromagent where it clingsby the attractive force of said permanent magnets, and a current pulseof the other polarity being effective to cause the electromagnet torepel said permanent magnets to allow said spring force to hold saidarmature against said disk braking any rotative action of said Shaftwhereby the brake is engageable and disengageable respectively by anelectric pulse of opposite polarity.
 2. A bi-stable brake device as setforth in claim 1 wherein said permanent magnets affixed to said armaturecap are oriented with polarity radially the same.
 3. A bi-stable brakedevice as set forth in claim 1 wherein said spring biased concentricnon-rotatable armature is held against rotation with respect to saidelectromagnet by light weight leaf material strips having opposite endsattached respectively to said outer annular pole piece and the outerperiphery of said armature.
 4. A bi-stable brake device as set forth inclaim 3 wherein said spring biased concentric non-rotatable armature isspring biased by a compression spring around said shaft supported withinsaid inner electromagnet pole.